Chromosomal abnormalities, namely deletion 11q-,13q-, 17p- and trisomy 12, have prognostic significance for patients with chronic lymphocytic leukemia (CLL). Several studies have demonstrated that the interphase fluorescence in situ hybridization technique (I-FISH) in CLL identifies such genomic aberrations in a higher frequency than classical karyotyping, including stimulated cultures using B-cell specific mitogens. However, there appears to be no information in the literature comparing I-FISH on non-cultured and cultured cells in CLL. A total of 56 samples from 49 patients with CLL were studied using commercially available probes for chromosomes 11q22.3(ATM), 13q14(13S272), 17p13(p53) and 12 centromere(D12Z3). We compared the results obtained by I-FISH-PBMC and those by interphase fluorescence in situ hybridization on TPA-stimulated peripheral blood cells (I-FISH-TPA) used for conventional cytogenetics in order to evaluate the usefulness of I-FISH-TPA. The proportion of abnormal nuclei obtained with the I-FISH-TPA was higher than that found with I-FISH-PBMC (P<0.001). Consequently, 15 cases with a negative or borderline result by I-FISH-PBMC became positive by I-FISH-TPA for deletion 11q- (n=2), 13q- (n= 9) and trisomy 12 (n=4). In all but one of these, chromosomal abnormalities were reconfirmed by either metaphase-FISH or conventional G-banding. Disease detection thus increased from 51% with I-FISH-PBMC to 78% with I-FISH-TPA. Interestingly, all 15 cases which reached the diagnostic thresholds for deletion 11q-,13q- and trisomy 12 had a slight lymphocytosis. An absolute lymphocyte count <8.7×109/l was found to be the critical threshold (P=0.037) below which I-FISH-TPA should be performed rather than I-FISH-PBMC. We have shown that I-FISH-TPA can not only detect a higher proportion of abnormal interphase nuclei but can also identify abnormal CLL cases which may be overlooked by I-FISH-PBMC, especially those with low absolute lymphocyte counts. I-FISH-TPA is thus a reliable technique for clinical diagnostics in CLL.

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